A new lower actinopterygian fish from the Upper Mississippian Bluefield Formation of West Virginia, USA

Abstract

The Upper Mississippian Bluefield Formation of the Mauch Chunk Group in southeastern West Virginia is known for its preservation of a variety of invertebrate taxa and early tetrapod trackways, but no lower actinopterygian remains have been formally described from these Carboniferous rocks. Here, the first lower actinopterygian fish is described from the Bluefield Formation of West Virginia. This fish is represented by a nearly complete articulated specimen with a three-dimensional snout and an unobstructed view of the gular and branchiostegal region. This new taxon is defined by a unique set of characters, which include features of the snout, circumorbital series, cheek, and operculo-gular region. These features make this fish different and distinct from previously described Carboniferous fishes. Some of the morphological features of note include the presence of a distinct lacrimal, premaxillary, ventral rostral and dorsal rostral bones, a narrow infraorbital ventral to the orbit, and a large crescent shaped infraorbital that contacts a single dermosphenotic. There is an anteriorly inclined hatchet-shaped preoperculum and six small suborbital bones anterior to the expanded region of this bone that filling the space between the preoperculum, dermosphenotic, and infraorbital. Posterior to the preoperculum, there is a single wedge-shaped dermohyal and a series of three rectangular anteopercular bones. The anteopercular bones extend halfway down the anterior border of the rectangular operculum. A median gular, two pairs of lateral gulars, and at least eight branchiostegal rays are present. The heterocercal caudal fin is deeply cleft and inequilobate. The scales have pectinated posterior margins and bear diagonal ridges of ganoine. The description of this new taxon represents the first actinopterygian and the first vertebrate body fossil described from the Bluefield Formation and the second actinopterygian taxon described from the Mauch Chunk Group in West Virginia.